Document U.S. Pat. No. 6,125,649 discloses a heat exchanging unit that can be used in a packaging to cool down a food or beverage being contained in it. The heat exchanging unit includes an external container and an internal container. The internal container has a plurality of thermally conductive discs in contact with an internal surface of it. An adsorbing material is arranged between the adjacent discs and is compacted between them in order to thus provide the maximum adsorbing material per unit of volume. The external surface of the internal container defines a plurality of grooves and is in contact with the internal surface of the external container. The grooves provide flow paths for a gas, such as carbon dioxide, which is fixed by adsorption on the adsorbing material in a first stage of filling of the internal container, to latter on flow and exit the heat exchanging unit to the outside when the user acts on a valve, the gas when expanding when thus exiting or escaping then withdrawing the heat being contained in the food or beverage being arranged in the container, and thus reducing its temperature.
A drawback of the heat exchanging unit of said document U.S. Pat. No. 6,125,649 is that the internal container, with the plurality of discs and the adsorbing material between them, is of complex and cost-intensive construction imposing a substantial bulk or size, the carbon dioxide having to be filled at a filling station. Besides, once used, it is not refillable and must be discarded together with the packaging. Another drawback is that the grooves that provide the above-mentioned flow path for the gas are rectilinear and parallel to the central axis of the internal and external containers, the flow path hence being the possibly shortest one. Although in the specification reference is made to the fact that the grooves can adopt a helical development, or another path there is no explanation whatsoever as to how to carry out said alternative form.
Document US 2005/0235657 describes an apparatus for cooling down a liquid in a portable container. The apparatus comprises a housing having an upper end and a lower end, this latter being possibly adapted to be fixed to the portable container. A pressurised gas reservoir or cartridge placed inside the housing has a supply valve to expel the pressurised gas. Heat exchanging fins are arranged around an outer surface of the gas reservoir or cartridge. When the gas is expelled, the reservoir or cartridge is cooled and the heat exchanging fins absorb heat from a liquid contained in the housing or passing through it.
Nevertheless, in this apparatus being described in the aforesaid document US 2005/0235657 the gas is directly expelled from the reservoir or cartridge to the atmosphere through a supply valve without following any path whatsoever in the inside of a heat exchanging unit, the cooling hence being not very efficient.
Therefore It is already known in the prior art quoted that the gas cartridge can be coupled to the inlet duct from the outside, or be placed in the inner side of the heat exchanger